Rock Forming Minerals are the common minerals that make up most of the rocks in the Earth’s crust (ex. quartz, feldspar, mica and calcite). There are over 2000 known minerals, but most of the rocks in the Earth’s crust are composed of only about 12 that are the most common.
Identification by Inspection
Color – the least useful property by itself, since many minerals have the same color. Also, some minerals are more than one specific color.
Luster – this is the way the mineral shines when light is reflected off of it. For the requirements of this course we will only need to distinguish between metallic and non-metallic lusters. Just keep in mind that metallic luster means the mineral shines like a metal.
Crystal Shape – this can be useful sometimes, as a few minerals have a very distinct, easily recognizable crystal shape (ex. calcite). The mineral grains found in rocks are often too small to identify by shape.
Identification by Simple Tests
Streak – this is the color of a mineral’s powder. To find the streak, rub the mineral on a white tile (streak plate). Often the color of the powder is not the same color as the mineral.
Cleavage – is the mineral’s tendency to break along flat surfaces. Examples include mica, halite, and calcite.
Fracture – is the mineral’s tendency to not break along flat surfaces. Often the mineral breaks in uneven or jagged pieces.
Hardness – this is the mineral’s resistance to being scratched. This is not whether or not the mineral can break! It is determined by doing comparison testing with substances of a known hardness and using Moh’s Hardness Scale. On this scale, common minerals are ranked in hardness from 1 to 10. A 10 on the scale is the hardest mineral (diamond).
Specific Gravity – is the weight of the mineral in air (actual weight), divided by the weight of the mineral in water. This calculation tells us how much more does the mineral weigh than an equal volume of water. *Since 1g of water takes up 1ml of volume, specific gravity is the same as density!
Acid Test – Some minerals will fizz when they come into contact with acids. One specific example is calcite (gives off CO² gas).
>
Special Properties – some mineral are magnetic, others have a distinct taste, some have fluorescence (glow in ultraviolet light) or phosphorescence (continue to glow after the light is removed), some are radioactive, and some even have double refraction (images appear twice when you look through these minerals (ex. calcite).
Properties of Common Minerals
The properties of common minerals can be found in the Reference Tables (last page).
How to Know the Minerals – Key Ideas
Rock Forming Minerals are the common minerals that make up most of the rocks in the Earth’s crust (ex. quartz, feldspar, mica and calcite). There are over 2000 known minerals, but most of the rocks in the Earth’s crust are composed of only about 12 that are the most common.
Identification by Inspection
Identification by Simple Tests
- Streak – this is the color of a mineral’s powder. To find the streak, rub the mineral on a white tile (streak plate). Often the color of the powder is not the same color as the mineral.
- Cleavage – is the mineral’s tendency to break along flat surfaces. Examples include mica, halite, and calcite.
- Fracture – is the mineral’s tendency to not break along flat surfaces. Often the mineral breaks in uneven or jagged pieces.
- Hardness – this is the mineral’s resistance to being scratched. This is not whether or not the mineral can break! It is determined by doing comparison testing with substances of a known hardness and using Moh’s Hardness Scale. On this scale, common minerals are ranked in hardness from 1 to 10. A 10 on the scale is the hardest mineral (diamond).
- Specific Gravity – is the weight of the mineral in air (actual weight), divided by the weight of the mineral in water. This calculation tells us how much more does the mineral weigh than an equal volume of water. *Since 1g of water takes up 1ml of volume, specific gravity is the same as density!
- Acid Test – Some minerals will fizz when they come into contact with acids. One specific example is calcite (gives off CO² gas).
>Special Properties – some mineral are magnetic, others have a distinct taste, some have fluorescence (glow in ultraviolet light) or phosphorescence (continue to glow after the light is removed), some are radioactive, and some even have double refraction (images appear twice when you look through these minerals (ex. calcite).
Properties of Common Minerals
The properties of common minerals can be found in the Reference Tables (last page).